The present invention relates to a method and apparatus for removing impurities, especially rust, from metallic objects. The method of the present invention constitutes an improvement over and a further development of the method which is disclosed in U.S. Pat. No. 4,368,080 granted Jan. 11, 1983 to Robert Langen et al.
The method which is disclosed in the patent to Langen et al. involves removal of oxidation products, especially rust, from metallic objects, particularly objects which contain or consist of iron or steel. The patented method involves the steps of focusing a laser beam upon rust to heat the rust to evaporation temperature and to thereby effect evaporation of rust from the surface of the metallic object. It has been found that such method is highly effective in that it allows for evaporation of oxidation products without adversely affecting the surface and/or the texture of the material of the object. Once the evaporation of oxidation products from a selected portion of the surface of a metallic object is completed, the thus exposed surface reflects a certain amount of the impinging radiation. The remainder of radiation is converted into heat which is rapidly dissipated by the object in all directions. Thus, short-lasting exposure of a relatively small portion of the object to a relatively large quantity of energy does not immediately lead to localized overheating of the metallic material and can be tolerated in many instances. As a rule, loose particles of rust and/or other oxidation products are mechanically removed in a first step and the remaining oxidation products are thereupon exposed to the action of a laser beam whose intensity is selected with a view to ensure evaporation of all traces of oxidation products but to avoid overheating of the metallic material adjacent to the thus exposed surface of the object. Thus, the rate of energy application to oxidation products is selected in such a way that it ensures total evaporation of rust or the like but to maintains the following heating of the metallic object within acceptable limits. In other words, there is a surplus of energy which is consumed in order to guarantee complete removal of impurities.